single substance breaks up into 2 or more simpler substances when it is heated

pg 180

combustion

when substance reacts with oxygen when heated to form one or more new substances

heat and light are given out here which can be used for cooking, transport and in generation of electricity in power stns pg 180

burning fuels such as coal, natural gas, petrol etc

in car engines, petrol burns in air to produce carbon dioxide, water vapour and heat. pg 181

oxidation

when charcoal burns, oxygen from air is added to carbon

addition of oxygen to substance

oxidation reactions also occur when other elements, metals and non metals burn in air

when magnesium burns in air, new substance, magnesium oxie is formed. this reaction is both combustion reaction(because magnesium burns in air) and oxidation reaction(because oxygen is added to magnesium)

eg, rusting of iron.iron combines with oxygen in air to form new susbtance--iron oxide or rust. iron+oxygen---> iron oxide(rust)

respiration

takes place in every cell in organism. in cell, food such as glucose, combines with oxygen and releases energy. during reaction, carbon dioxide and water are produced

pg 182

glucose molecules contain elements carbon, hydrogen and oxygen. during reaction, carbon and hydrogen combine with oxygen to form carbon dioxide and water

what happens when matter and light interact?

light is also involved in physical and chemical changes. sometimes, light causes changes.in other changes, light is given out

photosynthesis

process in which green plants use light energy to make food

pg 184

as glucose and oxygen are new substances, process of photosynthesis is chemical reaction

photography

coating on black and white photographic film contains silver bromide. exposure to light decomposes silver bromide into silver, which produces dark areas on on film

greater exposure to light, darker area on film

pg 185

what happens when matter and electricity interact?

physical changes: used for heating effect and magnetic effect of current

chemical changes:

electrolysis

use of electricity to cause chemical change

chemical effect of current

when electricity is passed through copper chloride, copper and chlorine are produced

pg 186

is used in process of electroplating. this is coating of object with thin layer of metal. negative electrode is covered with layer of copper metal in pg 186. eg, covering bicycle handlebars with thin layer of chromium or steel parts of car with zinc. this prevents rusting of handlebars and car

used to produce many useful products like household bleach and aluminium foil. pg 186

lightsticks

pg 187

light energy interacts with special dye in mixture to produce colored light. different lightsticks produce different colors because of different kinds of dyes in mixtures

What happens when substances mix

Changes occur when substances are mixed together. Eg, when sugar is added to water, physical change occurs—sugar dissolves to form sugar solution. Chemical changes may occur when mixed

Acids and metals

When dilute acids are mixed with certain metals, hydrogen gas and salt are produced

physical changes

no new substance is formed. physical change is change in which no new substance is formed. physical changes can be reserved. eg, water that is heated evaporates but they can be condensed again

why do changes occur?

because of interactions: may be between matter and energy, such as heat, light, or electricity. alternatively, interactions may be between different kinds of matter, such as when substances are mixed

what happens when subtances are mixed

changes can occur.

changes in matter take place around us all the time. these changes involve both living and non living matter. such changes, such as burning paper, are fast. others, such as rusting are slow

changes in matter also involve energy. by understanding these changes, we can better control them and use them to benefit our lives and environment. in this chapter, we look at interactions between matter and energy, types of changes and their effects